The aim of this investigation is to advance the understanding of the proliferative behavior of normal and neoplastic hematopoietic cells, by developing new and improved mathematical models of their growth and development. In close collaboration with Dr. B.D. Clarkson and his co-workers at Sloan-Kettering, we have commenced and/or will pursue investigations in the following directions. We are reinvestigating kinetic data that supposedly supports the existence of the Go or resting state in the cell cycle. We are going to examine quantitatively the proliferative and differentiation capacities of normal and neoplastic clonogenic cells obtained from human blood and marrow. We intend to study kinetic data of progenitor cells taken from the marrow of human marrow transplant recipients. We are developing a dynamical theory of cell populations observed by flow microfluorometric techniques.